A novel strategy is proposed to identify and initially characterize genes and interacting groups of genes which determine adult lifespan in the nematode C. elegans. The F1 progeny of crosses between C. elegans strains (e.g., N2xBO or N2xDH424) have lifespans similar to the parental strains, and yet F2's and derived inbred clones show increased variation in lifespans, which range from 70-160% of parental levels. This implies that multiple genes, polymorphic between these strains, determine C. elegans lifespan. We propose to characterize such genes by identifying alleles consistently present in the longest-lived recombinant inbred progeny of inter-strain crosses. Unique probes flanking those Tc1 transposons which are present in genomic DNA of the BO and DH424 strains, but absent from N2 and C12a, will be used to determine the source strain for homozygous regions of (N2 or C12a)x(BO or DH424) hybrid genomes. The allele ratio (- Tc1:+Tc1) must be 1:1 in the F1 heterozygotes, and any consistent shift between young worms at F1 and later generations would be attributed to reproductive selection favoring one allele. However, if a given allele ratio changes consistently between young adults and the longest-lived 5% of worms, both at the same generation (Fn greater than or equal to 12), this would indicate linkage between that polymorphic marker and a lifespan determining gene -- for which one of the two alleles conferred greater lifespan than the other. Polymerase chain reaction with multiplex primer sets, specific for sequences flanking mapped Tc1 elements in BO and/or DH424 DNA, will be used to analyze > 100 of the longest-surviving individual worms in such populations, to identify combinations of gene alleles which frequently co-segregate in long-lived worms. Comparison of these gene sets with those selected under conditions of hyperoxia or late fecundity, etc., will indicate the extent of overlap between the underlying genetic determinants for these traits. Identification of lifespan- modulating genes, and of alleles with differing contributions to longevity, will aid our understanding of the molecular mechanisms underlying senescence. In the long term, comparative studies of cognate genes in other species, including man, should reveal whether they share a common mechanism of senescence, and may implicate genetic interactions in the etiology of age-associated diseases.